Overlay proofing film

ABSTRACT

An improved overlay proofing film comprising a substantially transparent polyester base film which is first coated on one or both sides with a non-light sensitive composition having a refractive index of about 1.6, said non-light sensitive composition consisting essentially of a copolymer of polymethyl methacrylate and methacrylic acid.

This application is a division of U.S. patent application Ser. No.06/691,313 filed Jan. 14, 1985, now abandoned; and is a division of U.S.patent application Ser. No. 06/927,191 filed Nov. 4, 1986, now U.S. Pat.No. 4,748,101.

BACKGROUND OF THE INVENTION

This invention relates to an overlay proofing film having a base filmwith improved transparency. In the graphic arts, it is desirable toproduce a four or more color proof to assist a printer in correcting aset of color prints prior to using them to produce color plates and alsoto reproduce the color quality that will be obtained during the printingprocess. The proof must be a consistent duplication of the half tone,and should neither gain nor lose color. Visual examination of a colorproof should show the following characteristics:

1. Defects on the negative.

2. The best color rendition to be expected from press printing of thematerial.

3. The correct gradation of all colors and whether grays are neutral.

4. The need, if any, for subduing one of the colors and/or givingdirections for altering the film negatives before making the printingplates.

A method of transferring colored images has been applied to thepreparation of a color proofing sheet in multicolor printing. Thus,color proofing sheets, for multi-colored printing, have heretofore beenmade by using a printing press or a proof press while taking all thesteps necessary for actual multicolor printing, but such a conventionalmethod of color proofing has been costly and time consuming.

Photographic processes have also been used, especially photographicprocesses using photopolymers. The usual type of photographic colorproofing method is the overlay type.

In the overlay type of color proofing method, an independent transparentplastic support is used for producing a print of each color separationfilm by applying a photosensitive solution of the corresponding color,and a plurality of such supports carrying prints of corresponding colorsare then superimposed upon each other to produce a color proofing sheet.The overlay type of color proofing method has the disadvantage that thegrayness and density of the superimposed plastic supports tend to darkenthe color proofing sheet, and, as a result, the impression of the colorproofing sheet thus prepared becomes vastly different from copiesactually obtained by a conventional printing press or a proof press. Itsprimary advantage is that it is quick and can serve as a progressiveproof by combining any two or three colors in register.

As mentioned above, the typical proof sheet adapted for imagewise colorexposure consists in the most elementary form of a transparent basesheet coated on one side with a light sensitive composition containing adyestuff. Most commonly with negative acting materials, the lightsensitive composition may be composed of a diazo material, used eitheralone or in combination with a resinous binder, which composition iscaused to harden by exposure to a source of actinic light. The hardeningoccurs as the result of a photopolymerization, condensation, or couplingreaction which renders the light struck areas insoluble in commondeveloper solutions such as aqueous developers, while the non-lightstruck areas remain substantially chemically unaltered and soluble. Oncedeveloped, the light struck areas of the coating exposed through anegative transparency remain adhered to the base sheet in the form of animage.

In order to overcome the above-stated darkening problem, it is desiredthat a proofing film be obtained wherein the base film has improvedclarity and transparency.

SUMMARY OF THE INVENTION

This invention relates to an improved overlay proofing film. Moreparticularly, the invention relates to an improved overlay proofing filmcomprising a substantially transparent polyester base film which isfirst coated on one or both sides with a non-light sensitive compositionhaving a refractive index of less than about 1.6, said non-lightsensitive composition consisting essentially of a copolymer ofpolymethyl methacrylate and methacrylic acid, said coated polyester basefilm having a second coating on either side thereon, said second coatingcomprising a light sensitive mixture of

a. a resinous binder;

b. a colorant; and

c. a light sensitive material.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a proofing film wherein the polyesterbase film exhibits substantially improved transparency and clarity. Ingeneral, it has been found that a suitable anti-reflectance coating forpolyester film should be transparent and have a refractive index (R.I.)lower than the refractive index of the polyester film itself (R.I.=1.6).An oversimplification of the mechanism of this phenomena is that thelight that would normally bounce from surface to surface of the film nowcan be emitted through the lower refractive index coating giving theadvantage of improved film transparency.

The flexible polyester film of the present invention may be any flexiblefilm formed from any thermoplastic film forming polyester which isproduced by condensing a dicarboxylic acid or a lower alkyl diesterthereof with a glycol. Among the dicarboxylic acids and their loweralkyl diesters which may be employed to form a flexible polyester filmsupport are terephthalic; isophthalic; phthalic; 2,5-, 2,6, and2,7-naphthalene dicarboxylic; succinic; sebacic; adipic; azelaic;dibenzoic; the hexahydrophthalics; and bis-p-carboxyphenoxyethane. Oneor more of these acids and/or their lower alkyl diesters is reacted withone or more glycols which include ethylene glycol; diethylene glycol;1,3-propanediol; 1,4-butanediol; neopentyl glycol or1,4-cyclohexanedimethanol. Since one or more diesters may be reactedwith one or more glycols, the polyester film of this invention is notlimited to homopolyesters, but also includes mixed polyesters such ascopolyesters.

Of the film forming polyesters within the contemplation of thisinvention, preferred are those containing at least a major amount ofpolyethylene terephthalate, the most preferred being polyethyleneterephthalate. Polyethylene terephthalate film is formed from a polymerproduced by polymerization of bis-(2-hydroxyethyl) terephthalate.Bis-(2-hydroxyethyl) terephthalate is itself formed as an intermediateby one of two different methods. One method for producingbis-(2-hydroxyethyl) terephthalate is by direct esterification ofterephthalic acid with ethylene glycol as described in U.S. Pat. No.3,050,533. In this method, the by-product of the reaction is water whichis distilled from the reaction product. A second method for producingbis-(2-hydroxyethyl) terephthalate is by transesterification of adialkyl ester of terephthalic acid, preferably dimethyl terephthalate,with ethylene glycol. Preferably, two molecular proportions of ethyleneglycol react with one molecular proportion of the dialkyl terephthalate.More preferably, more than two molecular proportions of ethylene glycolper molecular proportion of the dialkyl terephthalate are used sinceunder these conditions the initial transesterification reaction occursmore rapidly and completely. The transesterification reaction isconducted under conditions of elevated temperature. For example, atemperature in the range of between about the boiling temperature of thereaction mixture to as high as about 250° C. may be used. The reactioncan occur at atmospheric, sub-atmospheric or super-atmospheric pressure.The by-product of the transesterification reaction is an alkanol. Forexample, if dimethyl terephthalate is used, methanol is produced. Thealkanol is removed from the reaction product. In order to increase thereaction rate, many known catalysts may be employed in thetransesterification reaction, as desired.

After the bis-(2-hydroxyethyl) terephthalate has been produced, it maybe converted to polyethylene terephthalate by heating at a temperatureabove the boiling point of the ethylene glycol or the reaction mixtureunder conditions affecting the removal of the glycol or water. Theheating may occur at a temperature as high as about 325° C., if desired.During heating, pressure is reduced so as to provide rapid distillationof the excess glycol or water. The final polyethylene terephthalatepolymer may have an intrinsic viscosity, as measured inorthochlorophenol at 25° C., in excess of about 0.3 deciliter per gram.More preferably, the intrinsic viscosity of the polymer ranges fromabout 0.4 to about 1.0 deciliter per gram, again measured inorthochlorophenol at 25° C. Still more preferably, the polyethyleneterephthalate employed in the present invention has an intrinsicviscosity of about 0.5 to about 0.7 deciliter per gram as measured inorthochlorophenol at 25° C.

In a preferred embodiment, the polyester film forming polymer is meltedand thereafter extruded onto a polished revolving casting drum to form acast, flexible sheet of the polymer. Thereafter, the film is axiallystretched in one direction, either in the direction of extrusion(longitudinal), or perpendicular to the direction of extrusion(transverse) in the case of monoaxially oriented film, and in twodirections in the case of biaxially oriented film, that is, the film isstretched in both the longitudinal and transverse directions. The firststretching step of the cast sheet may be in either or these twoorthogonal directions. The amount of stretching, to impart strength andtoughness to the film, can range from about 3.0 to about 5.0 times theoriginal cast sheet dimension in one or both directions. Preferably, theamount of stretching is in the range of between about 3.2 and 4.2 timesthe original dimension. The stretching operations are carried out attemperatures in the range of from about the second order transitiontemperature to below the temperature at which the polymer softens andmelts. It is important that the stretching temperature is above theglass transition temperature of the film. The film is then crystallizedby heating to a temperature of from about 130° C. to about 240° C.,preferably 150° C. to 180° C., while being transversely restrained butwithout film stretching. Crystallizing is normally complete when thistreatment is performed for about five seconds or more. The film is thencooled to substantially ambient atmospheric room temperature. The thuslyproduced film may have a thickness of from 0.48 to 30 mils, preferbly 1to 9 mils, most preferably 3 to 7 mils.

The thusly formed polyester film is then coated with a non-lightsensitive first coating composition having a refractive index of lessthan about 1.6 which consists essentially of a copolymer of polymethylmethacrylate and methacrylic acid. The use of the term "consistsessentially of" is meant to exclude from the non-light sensitivecomposition any materials which, if present, would seriously detractfrom the composition's ability to render polyester film moretransparent. The components of the copolymer may be present in roughlyequal amounts but it is preferred that polymethyl methacrylate comprisethe majority of the copolymer. Most preferably, the copolymer comprisesabout 80% to about 95% of polymethyl methacrylate and about 5% to about20% of methacrylic acid.

The polymethyl methacrylate/methacrylic acid copolymer of this inventionmay be manufactured by any conventional method known to the polymerchemist, for instance by solution polymerization or dispersion (oremulsion) polymerization, such as described in U.S. Pat. No. 4,465,572and 4,430,419. Preferably, the copolymer is manufactured by solutionpolymerization, as this obviates the need to filter the coating solutionprior to coating.

The first coating composition may optionally include a curing agent forcuring the copolymer. Although curing the copolymer has no significanteffect on the improved transparency of the polyester base film, to do sowill help the first coating to adequately resist the solvent system of alight-sensitive mixture applied thereon. Preferred curing agents are thepolyfunctional aziridines. Specific curing agents which are useful inthe practice of this invention includetrimethylolpropane-tris-(β-(N-aziridinyl) propionate), which isavailable as XAMA-2 from Cordova Chemical Company of North Muskegon,Mich., and pentaerythritol-tris-(β-(N-aziridinyl) propionate), which isavailable as XAMA-7 from Cordova Chemical Company of North Muskegon,Mich. If desired, an accelerator for the cure of the copolymer may alsobe added to the first coating, such as triethanolamine.

The first coating may be applied to the polyester base film by forming asolution or dispersion of the coating materials in suitable solvent(s).Solvents should be selected based on the solubility characteristics ofthe coating materials. Suitable solvents include dimethyl sulfoxide,dimethyl formamide, tetrahydrofuran, glycol ethers such as propyleneglycol mono methyl ether, ethylene glycol mono methyl ether and ethyleneglycol mono ethyl ether, esters such as ethyl acetate, butyl acetate andamyl acetate, ketones such as methyl ethyl ketone, cyclohexanone anddiacetone alcohol, and mixtures of the above. Coating may be effected byany of the techniques well known to those skilled in the art, such as byroller coating, slot coating, spray coating, gravure coating or kisscoating. Preferably, the polyester film is coated with the first coatingby means of kiss coating. The solvents may then be dried off by methodsknown to those skilled in the art, although some residue may remain.

In the preferred embodiment, the film is coated with the first coatingat a coating weight of at least about 0.5 g/m². The upper coating weightlimit is that above which the film shows inflexibility and the tendencyto crack on handling and is generally about 7.0 g/m². More preferbly,the first coating is present at a coating weight of from about 1.0 g/m²to about 6.0 g/m² and most preferably is about 20 g/m² to about 5.0g/m². Additionally, it is preferred that the first coating be coated onboth sides of the polyester film since film coated on both sides showsimproved transparency over film coated on one side only, although eachshow substantial improvement over uncoated film.

The polyester film coated with the first coating is then coated with asecond coating which comprises a light sensitive mixture of

(a) a resinous binder;

(b) a colorant; and

(c) a light sensitive material.

The components of the light sensitive mixture of the present inventionmay be the conventional components which are known in the art for suchcoatings used in positive acting or negative acting light sensitivesystems. The resinous binder material may be any of the known prior artbinders which have been disclosed either for positive acting or negativeacting light sensitive coating compositions.

In negative acting systems, the binder material may be relatively inertto photochemical reaction, serving merely as a carrier for the lightsensitive materials, colorants, and other additives which may be presentin the coating composition. Exemplary of suitable binder materialsinclude cellulose esters such as cellulose acetate, cellulose acetatesuccinate and cellulose acetate butyrate; polyvinyl actals such aspolyvinylbutyral and polyvinyl formal; polyamide resins; copolymers ofvinyl chloride with polar monomers such as acrylonitrile, acrylic ofmethacrylic acid of their esters, and with vinyl acetate; polymericesters such as polyvinyl acetate or copolymers of vinyl acetate withacrylic acid, methacrylic acid and their esters, or with maleic acid ormaleic anhydride; copolymers of styrene with acid functional comonomerssuch as ethyl acrylate, vinyl acetate and maleic anhydride; naturalpolymers such as gelatin, casein or fish glue; polyvinyl alcohol;polyacrylamides; and like materials. In a positive acting system, theresinous binder materials most commonly employed are selected fromalkali soluble resins such as phenol/formaldehyde novolak resins andlike materials. Preferably, the binder material is a copolymer ofpolymethyl methacrylate and methacrylic acid.

The coloring agents employed in the present invention include thosedyestuffs and pigments which are known in the art and which have colorssubstantially identical with the standard colors of ink required forcolor proofing, e.g. yellow, cyan, magenta and black. Examples ofsuitable colorants include Grasol Fast Yellow 5FL (C.I. Solvent Yellow27), Grasol Fast Rubine 2BL (C.I. Solvent Red 128), Victoria Pure BlueFGA (C.I. Basic Blue 81), Neozapon Yellow GG (C.I. Solvent Yellow 79),Neozapon Fast Red BE (C.I. Solvent Red 122), Sudan Blue II (C.I. SolventBlue 35-C.I. 6155(S), Victoria Cyan F6G (C.I. 42025), Rhodamine FB (C.I.45170), Rhodamine 6GDN Extra (C.I. 41560), Auramine Concentrate (C.I.41000), carbon black and like materials.

Light sensitive materials which are preferably used in the practice ofthe present invention include any suitable light-sensitive diazoniumsalt which are well known to the skilled artisan. Preferred are thepolymeric diazonium compounds including those condensed withformaldehyde such as disclosed in U.S. Pat. Nos. 2,063,631 and2,667,415, the polycondensation products such as disclosed in U.S. Pat.Nos. 3,849,392 and 3,867,147, and the high speed diazos such asdisclosed in U.S. Pat. No. 4,436,804, all of which are herebyincorporated herein by reference.

The most preferred of these diazonium salts is the condensation productof 3-methoxy-4-diazo diphenyl amine and 4,4'-bis-methoxy methyl diphenylether, isolated as the mesitylene sulfonate, such as is taught in U.S.Pat. No. 3,849,392.

Other compositions useful as the light sensitive material of thisinvention include those photomonomers or oligomers in conjunction with aphotoinitiator wherein the solvent system used to apply them to the filmis not so hard or severe as to interfere with the non-light sensitivecomposition already coated on the film.

It is to be emphasized that the specific light sensitive compositionswhich may be employed in the present invention are conventional in theart and should be selected by one skilled in the art based oncompatibility and operability in the binder system disclosed herein.

The light sensitive coating compositions may be most convenientlyapplied to the film substrate by forming a solution or dispersion of thecoating ingredients in suitable solvent(s), applying the desiredquantity of the solution to the surface of the film by any suitabletechnique such as roller coating, dip coating, miniscus coating, doctorblade coating or whirler coating, and drying to evaporate the solventalthough there may be some residue remaining. The light sensitivecoating composition may be coated on either side of the coated polyesterbase film, even if the non-light sensitive first coating is coated ononly one side of the polyester base film. Suitable solvents which may beemployed should be selected based on the solubility characteristics ofthe light sensitive compositions and include dimethyl sulfoxide,dimethyl formamide, tetrahydrofuran, glycol ethers such as propyleneglycol mono methyl ether, ethylene glycol mono methyl ether and ethyleneglycol mono ethyl ether, esters such as ethyl acetate, butyl acetate andamyl acetate; ketones such as methyl ethyl ketone, cyclohexanone anddiacetone alcohol, and mixtures thereof.

The composition of the coating on a dry basis generally should range inthe order of about 25 to 75% by weight of binder material. An effectiveamount of a colorant is generally in the range of about 2 to 15% byweight and effective amounts of the light sensitive materials as areknown in the art. The concentration of the solids in the coatingsolution prior to application to the substrate and drying depends uponthe coating method used in depositing the coating, but generallysolutions containing from about 2 to 20% by weight solids aresatisfactory.

In the preferred embodiment, the second coating is present at a coatingweight of from about 3.5 g/m² to about 7.5 g/m². More preferably, thesecond coating is present at about 4.0 g/m² to about 6.0 g/m². The mostpreferred coating weight for the second coating is about 5.0 g/m².

The thusly prepared overlay proofing film may then be exposed to actiniclight through a suitable mask or contact flat and then developed with anaqueous alkaline developer. Suitable developers may include componentssuch as monosodium phosphate, trisodium phosphate and the sodium sulfatederivative of 7-ethyl-2-methyl-4-undecanol.

The following examples illustrate the fact that although other coatingsalso have a refractive index (R.I.) lower than polyester film, thecoatings of this invention are the ones which may be used successfullyto form a proofing film with increased transparency. It is to beunderstood that the following examples are merely illustrative of theinvention, which should not be limited thereto.

EXAMPLE 1

Thin films of five different coating resins, each having an R.I. lessthan polyester film are coated on Melinex 516, a polyester film subbedwith nodules of silica to facilitate handling and eliminate the effectsof static, obtained from I.C.I., and the resultant films checked foropacity, ability to be wet by light-sensitive topcoat and solventresistance. The results are shown in Table 1.

                  TABLE 1                                                         ______________________________________                                        Coating            R.I.   Comments                                            ______________________________________                                        (1) Polytetrafluoroethylene                                                                          1.35   too opaque; light-                                                            sensitive coating will                                                        not wet the surface;                                                          solvent resistance                                                            acceptable                                      (2) Silicones          1.43   transparent but will                                (Syl-off 294 obtained from                                                                              not wet with light-                                 Dow-Corning)              sensitive coating;                                                            solvent resistance                                                            acceptable when                                                               crosslinked                                     (3) 85% Polymethyl methacrylate                                                                      1.49   transparent; will wet;                              15% Methacrylic Acid      solvent resistant                                   (prepared by dispersion   acceptable when                                     polymerization)           crosslinked                                     (4) 95% Polymethyl methacrylate                                                                      1.49   Transparent; will wet;                              5% Methacrylic acid       solvent resistance                                  (prepared by dispersion   acceptable when                                     polymerization)           crosslinked                                     (5) 85% Polymethyl methacrylate                                                                      1.49   Transparent; will wet;                              15% Methacrylic Acid      solvent resistance                                  (prepared by solution     acceptable when                                     polymerization)           crosslinked                                     ______________________________________                                    

The coatings of this invention (3, 4 and 5) are the only ones which showacceptable performance when a light sensitive topcoat is applied.

EXAMPLE 2

23.75 g of a copolymer of 85% polymethyl methacrylate/15% methacrylicacid prepared by conventional dispersion polymerization (10% solids inmethyl cellosolve) is dissolved in a 50/50 mixture of methyl cellosolveand methyl ethyl ketone (525 g) under moderate stirring and gives aclear solution. 0.5 g of triethanolamine is then added and stirringcontinued. 1.25 g of trimethylolpropane-tris-(β-(N-aziridinyl)propionate) is then added to the formulation and the stirring continuedfor a period of 30 minutes to insure complete mixing. The solution isthen filtered through a #4 Whatman filter paper before coating. Thesolution is then coated on both sides of 3 mil Melinex 516 polyesterfilm at a coating weight of 0.5 g/m² using a kiss coating method ofapplication. The coated film is then placed in an oven for about 1minute at a drying temperature of 275° F. The transparency of theresultant film is then measured spectrophotometrically on an IBM-7410spectrophotometer. The results are shown in Table 2.

EXAMPLE 3

A coating solution is prepared as described in Example 2 and coated onboth sides of a 3 mil Melinex 516 polyester film at a coating weight of1 g/m². The transparency of the resultant film is then determined byspectrophotometric transmission readings on an IBM-7410spectrophotometer. The results are shown in Table 2.

EXAMPLE 3A

A coating solution is prepared and coated as described in Example 3except that the triethanolamine andtrimethylolpropane-tris-(β-(N-aziridinyl) propionate) components areomitted, thereby resulting in an uncured coating. The transparency ofthe resultant film is then determined by spectrophotometric transmissionreadings on an IBM-7410 spectrophotometer. The results are shown inTable 2.

EXAMPLE 4

A coating solution is prepared as described in Example 2 and coated onboth sides of a 3 mil Melinex 516 polyester film at a coating weight of2 g/m². The transparency of the resultant film is then determined byspectrophotometric transmission readings on an IBM-7410spectrophotometer. The results are shown in Table 2.

EXAMPLE 4A

A coating solution is prepared and coated as described in Example 4except that the triethanolmine andtrimethylolpropane-tris-(β-(N-aziridinyl) propionate) components areomitted, thereby resulting in an uncured film. The transparency of theresultant film is then determined by spectrophotometric transmissionreadings on an IBM-7410 spectrophotometer. The results are shown inTable 2.

EXAMPLE 5

A coating solution is prepared as described in Example 2 and coated on a3 mil Melinex 516 polyester film at a coating weight of 6 g/m². Thetransparency of the resultant film is then determined byspectrophotometric transmission readings on an IBM-7410spectrophotometer. The results are shown in Table 2.

EXAMPLE 6

A coating solution is prepared as described in Example 2 and coated onboth sides of a 3 mil Melinex 516 polyester film at a coating weight of7 g/m². The transparency of the resultant film is then determined byspecrophotometric transmission readings on an IBM-7410spectrophotometer. The results are shown in Table 2.

EXAMPLE 7

A coating solution is prepared as described in Example 2 and coated onone side of a 3 mil Melinex 516 polyester film at a coating weight of 2g/m². The transparency of the resultant film is then determined byspectrophotometric transmission readings on an IBM-7410spectrophotometer. The results are shown in Table 2.

EXAMPLE 8

409 gm of a copolymer of 85% polymethyl methacrylate/15% methacrylicacid prepared by conventional solution polymerization (36% solids inmethyl ethyl ketone) is dissolved in 712 gm of propylene glycol monomethyl ether and 446 gm of methyl ethyl ketone under moderate stirring.1.5 g of triethanolamine is then added, followed by 4.27 g oftrimethylolpropane-tris-(β-(N-aziridinyl)propionate) and the stirringcontinued for 10 minutes to insure complete mixing. The solution is thencoated on both sides of 3 mil Melinex 505, a polyester film subbed withan adhesion promoter to improve clarity, obtained from I.C.I., at acoating weight of 4.3 gm² using a kiss coating method of application.The coated film is then placed in an oven for about 1 minute at a dryingtemperature of 275° F. The transparency of the resultant film is thenmeasured spectrophotometrically on an IBM-7410 spectrophotometer. Theresults are shown in Table 2.

                  TABLE 2                                                         ______________________________________                                        Example   Transmission  Comments                                              ______________________________________                                        Uncoated Film                                                                           .059                                                                2         .028          Newton rings visible                                  3         .037          Newton rings visible                                  3A        .037          Newton rings visible                                  4         .037          Essentially negligible                                                        Newton ring effect                                    4A        .037          Essentially negligible                                                        Newton ring effect                                    5         .038          No Newton rings visible                               6         .040          Film cracking evident                                 7         .046          Essentially negligible                                                        Newton ring effect                                    8         .036          No Newton rings visible                               ______________________________________                                    

In the above data it is evident that the transparency of polyester filmis improved by applying the coating of this invention. While the coatingof one side alone improves the transparency substantially, the coatingof both sides shows the greatest improvement.

EXAMPLE 9

A light sensitive composition is prepared by dissolving 2.7 g of acopolymer of 85% polymethyl methacrylate/15% methacrylic acid binder ina solvent mixture comprising 35 g of methyl ethyl ketone, 20 g ofpropylene glycol methyl ether, and 20 g of diacetone alcohol undermoderate stirring. The following dyes are then added: 0.4 g of calcozineyellow, 0.2 g of Rhodamine GDN and 0.1 g of Victoria Pure blue, whilemixing. While the solution is still being mixed, 3.5 g of thecondensation product of 3-methoxy-4-diazo diphenyl amine sulfate and4,4'-bis-methoxy methyl diphenyl ether isolated as the mesitylenesulfonate is added followed by 3.0 g of hydroxy propyl celluloseavailable as Klucel MF from Hercules Corp. The entire formulation isstirred for thirty minutes after all the components have been added toinsure complete mixing.

Meyer bar drawdowns are then used to apply this formulation to the filmsprepared in examples 3 and 4 at differing coating weights. The coatedfilms are then exposed through a negative for twenty units on aBerkey-Ascor exposure unit and developed by hand with an aqueousalkaline developer comprising trisodium phosphate, monosodium phosphate,the sodium sulfate derivative of 7-ethyl-2-methyl-4-undecanol availableas Niaproof 4 from Niacet Co. and water. The transparency of a clearportion of the resultant film is then measured by spectrophotometrictransmission readings on an IBM-7410 spectrophotometer. The results areshown in Table 3.

                  TABLE 3                                                         ______________________________________                                        Film from Example                                                                            Coating Weight                                                                            Transmission                                       ______________________________________                                        3              4.25 g/m.sup.2                                                                            .036                                               3              5.05 g/m.sup.2                                                                            .037                                               4              5.52 g/m.sup.2                                                                            .037                                               ______________________________________                                    

No significant increases in the transmission values of the films areseen after imaging of the light sensitive top coat.

EXAMPLE 10

A light-sensitive composition is prepared by blending together 210 g ofmethyl ethyl ketone, 94.5 g of propylene glycol mono methyl ether and140 g of diacetone alcohol under moderate stirring and then adding 21 gof Scripset 540, a styrene/maleic acid half ester copolymer having anaverage molecular weight from about 10,000 to 50,000 available fromMonsanto, and stirring until the copolymer is dissolved. 1.75 g ofp-toluene sulfonic acid and 10.5 g of the condensation product of3-methoxy-4-diazo diphenyl amine sulfate and 4,4'-bis-methoxy methyldiphenyl ether isolated as the mesitylene sulfonate are then added whileunder continued stirring. In a separate vessel, 122.5 g of a whitedispersion (50% solids in propylene glycol mono methyl ether) and 42 gof a black dispersion (25% solids in methyl ethyl ketone) are blended.The first mixture is then added to the dispersion blend and the entireformulation is stirred for thirty minutes to insure complete mixing.

This formulation is then applied to the film prepared in Example 8 byminiscus coating at a coating weight of 5.1 g/m². The coated film isthen exposed through a negative for twenty units on a Berkey-Ascorexposure unit and developed by hand with the developer described inExample 9. The transparency of a clear portion of the resultant film isthen measured by spectrophotometric transmission readings on an IBM-7410spectrophotometer. This results in a transmission reading of 0.037.

Again, no significant increases in the transmission values of the filmsare seen after imaging of the light sensitive top coat.

I claim:
 1. A substantially transparent polyester film having improvedtransparency, said polyester film having a substantially transparentnon-light sensitive coating directly coated thereon, said coatingconsisting essentially of a copolymer of polymethyl methacrylate andmethacrylic acid having a refractive index of less than about 1.6. 2.The film of claim 1 wherein said polyester film comprises a film ofpolyethylene terephthalate.
 3. The film of claim 1 wherein said coatingfurther comprises a curing agent for the copolymer.
 4. The film of claim3 wherein said curing agent comprises a polyfunctional aziridine.
 5. Thefilm of claim 4 wherein said curing agent is selected from the groupconsisting of trimethylolpropane-tris-(β-(N-aziridinyl) propionate) andpentaerythritol-tris-(β-(N-aziridinyl) propionate.
 6. The film of claim3 wherein said coating further comprises an accelerator for the cure ofsaid copolymer.
 7. The film of claim 6 wherein said accelerator istriethanolamine.
 8. The film of claim 1 wherein said copolymer comprisesabout 80% to about 95% by weight of polymethyl methacrylate and about 5%to about 20% by weight of methacrylic acid.
 9. The film of claim 8wherein said copolymer comprises about 85% by weight of polymethylmethacrylate and about 15% by weight of methacrylic acid.
 10. The filmof claim 8 wherein said copolymer is coated on both sides of saidpolyester film.
 11. The film of claim 8 wherein said copolymer comprisesabout 95% by weight of polymethyl methacrylate and about 5% by weight ofmethacrylic acid.
 12. The film of claim 11 wherein said copolymer iscoated on one side of said polyester film.
 13. A substantiallytransparent polyester film having improved transparency, said polyesterfilm having a substantially transparent non-light sensitive compositiondirectly coated thereon, said coating composition consisting essentiallyof a copolymer of polymethyl methacrylate and methacrylic acid whereinsaid copolymer comprises at least about 50% by weight, based on theweight of said copolymer, polymethyl methacrylate and wherein saidcoating composition has a refractive index of less than about 1.6. 14.The film of claim 13 wherein said copolymer comprises from about 80% toabout 95% by weight, based on the weight of said copolymer, polymethylmethacrylate and from about 5% to about 20% by weight, based on theweight of said copolymer, methacrylic acid.
 15. The film of claim 13wherein said coating composition further comprises a curing agent forsaid copolymer in admixture therewith.
 16. The film of claim 15 whereinsaid copolymer comprises from about 80% to abut 95% by weight, based onthe weight of said copolymer, polymethyl methacrylate and from abut 5%to about 20% by weight, based on the weight of said copolymer,methacrylic acid.
 17. The film of claim 15 wherein said curing agent isselected from the group consisting oftrimethylolpropane-tris-(β-(N-aziridinyl) propionate) andpentaerythritol-tris-(β-(N-aziridinyl) propionate).
 18. The film ofclaim 17 wherein said coating composition further comprisestriethanolamine.
 19. The film of claim 15 wherein said coatingcomposition further comprises an accelerator in admixture therewith. 20.The film of claim 19 wherein said accelerator is triethanolamine.